1. Field of the invention
The present invention relates to a signal processing processing apparatus for rotation sensors for outputting a signal representing information concerning the rotational condition of a member being detected by the use of a magnetic-electric transducing element.
2. Description of the prior art
For use in detecting the rotational speed of an internal combustion engine, Japanese Utility Model Application Public Disclosure No. 29713/88 discloses a signal generator having a magnetic rotary member having N poles and S poles alternately provided on its periphery in an annular form and a magnetic-electric transducing element for producing an electric signal corresponding to changes in the magnetic field caused by the rotation of the magnetic rotary member. In the disclosed signal generator, part of the output signal obtained from the transducing element is inverted in phase to obtain two signals different only in a phase, the level of each signal is discriminated by a corresponding level comparing circuit with hysteresis characteristics, and the time that the magnetic rotary member moves relative to the transducing element such that the transducing element moves relatively from a position facing N or S pole of the magnetic rotary member to a position facing S or N pole thereof is detected by processing of the output signals of the level comparing circuits.
The disclosed signal generator requires an inverting amplifying circuit for obtaining two signals different only in being separated in phase by 180 degrees. Thus, if the adjusted offset of the inverting amplifying circuit should shift from the desired condition, the signal generator will no longer be able to produce a signal properly representing the rotational condition of the magnetic rotary member. Furthermore, since the proposed signal generator is arranged to generate a set of pulse signals alternating in polarity, it will be difficult to remove noise components from these pulse signals when the pulse width of the individual pulse signals is shortened due to increase in the rotational speed of the magnetic rotary member, making it impossible to use the signal at a remote point. Still further, it is difficult to determine the exact rotational position of the magnetic rotary member when it is subject to vibration of a relatively small angular amplitude during rotation.